1. Field of the Invention
The present invention relates to a switching-type vertical deflection output circuit having a pump-up circuit added to the switching-type vertical deflection output circuit in the vertical deflection circuit of television receivers and other devices using a cathode ray tube.
2. Description of the Related Art
Generally, in vertical deflection output circuits mounted in television receivers, etc., after a sawtooth voltage generated in a vertical oscillation circuit has been shaped and amplified in a vertical drive circuit, it is further amplified in a vertical deflection output circuit to output a vertical deflection sawtooth current to a vertical deflection coil. Then, a magnetic field is generated in an image receiving tube by supplying the sawtooth current to the vertical deflection coil and an electron beam is deflected upward and downward. In the vertical deflection circuit, the vertical deflection output circuit which supplies the amplified sawtooth current to the vertical deflection coil is important in displaying normal images on the image receiving tube.
In recent years, there is a tendency to construct the vertical deflection circuit by using a switching-type amplifier from the view point of operation efficiency. This is because the operation efficiency of the switching-type amplifier is theoretically 100%, and thus, the amplifier has a high operation efficiency.
On the other hand, in the vertical deflection circuit of television receivers using a cathode ray tube, a so-called pump-up circuit, in which, in order to shorten the flyback period, the power-supply voltage is increased only during the flyback period, is widely used. As a vertical deflection output circuit which is already commercially available, for example, a pump-up circuit is incorporated in a semiconductor integrated circuit STV9380 manufactured by STMicroelectronics.
In the switching-type vertical deflection output circuit, when a pump-up circuit is added, there is a problem that disturbance is caused in the vertical deflection output waveform when switched from the flyback period to the scanning period.
A switching-type vertical deflection output circuit in which, even if a pump-up circuit is added, disturbance is not caused in the vertical deflection output waveform when switched from the flyback period to the scanning period has been proposed.
For example, in Japanese Unexamined Patent Application Publication No. 9-181932, the above problem is solved as described below: In order to dissolve disturbance in the waveform right after the pump-up period in a switching-type vertical deflection output circuit, an optimal control is performed so that the end of the pump-up period may be delayed for a fixed time by using a monostable multivibrator circuit.
However, in the integrated circuit in which a pump-up circuit is already used in the vertical deflection circuit, there are cases where it is difficult to alter the pump-up circuit itself, as described in Japanese Unexamined Patent Application Publication No. 9-181932.